A common kind of sash lock cooperates with a keeper to tighten and lock a window. The keeper is mounted to one sash of a double-hung window. The sash lock has a rotatable cam mounted on a housing that is connected to the other sash of the window. Rotating the cam causes a finger which is part of the cam to move across the gap between the two sashes, engage a keeper mounted on the other sash and draw the sashes toward each other while forcing one sash up and the other down. This style of sash lock is common and quite old. It is also vulnerable to being forced open. In particular, it may be possible with some prior art sash locks to force a knife blade or similar tool into a crack between the two sashes, engage the cam with the blade, and force the lock to an open position.